Processes for improving the corrosion resistance of ni-co-metal coatings containing boron



April 19, 1966 HElNZ-GUNTER KLEIN ET AL Filed June 20, 1962 Metal article to be plated plating Corrosion resistant treatment according to the invention (aqueous soiutlon 0P nexavalent Cr compound) Water rinsing Corrosion resistant Cnerriicai N1 and/or Co rnetai boron plated rnetai article 3,247fi PROCESSES FOR IMPROVING THE CORROSION RESISTANCE OF NI-CO-METAL COATINGS CONTAINING BORON HEINZ-GUNTER KLEIN EBERHARD ZIRNGIEBL 5y 3W5 TD/ whee ig rwmg/ ATTOR N575 United States Patent Ni-Co-metal-boron coatings are formed by chemical plating of metal surfaces in plating baths containing as essential components the metal salts, complex formers and, as a reducing agent, boron-hydrogen compounds with one tofour hydrogen atoms linked directly to boron. Nothing is so far known from publications about the corrosive behavior of these metal-boron layers, for example nickel-boron or cobalt-nickel-boron layers, etc.

'The metal-boron coatings 'do not display any pores under the microscope or interference microscope, the ferroxyl test, however, indicates the existence of active .pOintS so that pitting and further corrosion cannot be completely excluded, under certain conditions. 5

The object of the invention is to provide a process for improving the corrosion resistance of chemically deposited Ni-Co-metal coatings containing boron, characterized by after-treating the chemically plated metal surfaces with aqueous solutions containing a hexavalent chromium compound, preferably chromic acid and, if desired, phosphoric acid or its salts.

The process is illustrated by the flow diagram shown in the drawing.

The duration of the after-treatment, the concentration of the hexavalent chromium compounds as well as the bath temperature can be varied within a wide range. The temperature of the after-treatment bath can lie between room temperature and boiling temperature, the concentration of, for example chromic acid can be 1 to 300 g./liter. As an addition to the bath, in order to shorten the duration of stay, 0.1 to 2% phosphoric acid are sufficient.

In order to achieve a good protection against corrosion a coating of 5 ,u of a NiB alloy, containing 90% Ni and 10% B, an after-treatment of 5 minutes at 40 C. in a Patented Apr. 19, 1966 bath of the composition 200 g./liter CrO and 5 g./liter H PO is technically satisfactory. For a coating of 10 p. a duration of stay of 8 minutes at C. in the same bath is required. Investigations of the coatings carried out subsequent to the after-treatment show that the active points detected in the ferr-oxyl test have completely disappeared. The corrosive behavior of the surfaces treated according to this invention surpasses that of objects metallized by galvanic methods as well as of those metallized using alkali metal hypophosphite as a reducing agent.

The following examples are given for the purpose of illustrating the invention:

Example 1 In a chemical plating bath of the following composition:

30 g./ liter of nickel chloride 40 g./ liter of sodium hydroxide 50 g./ liter of ethylene diamine 0.6 g.'/liter of sodium borohydride 1 g./liter of thiodiglycollic acid 10 mg./liter of lead chloride v C. The residing time of the plates in the bath was 10 minutes. Subsequently, the plates were rinsed with water and subjected to the corrosion test.

The corrosion test was carried out using the corrosion apparatus Testor of the Firma 'Kohler, Lipperode, at

50 C. and relative humidity of the air. The samples were suspended from glass hooks in the apparatus. During the test period a thin layer of condensed water was always present on the sample surface. The duration of the test was 15 days. The samples were examined first at short intervals, later at longer intervals and the degree of rusting was estimated as a percentage of the total surface. The individual degrees of rusting in proportion to the period of testing are shown in the table.

Rust as percent of surface Sample No. G.-dep0sit Ni-B/dm. Aftertreated 1 h. 5 h. 1 day 3 days 5 days 10 days 15 days 1.0998 (ca. 0 0 0 0 0 0 0.1 1.0409 (ca. 15 0 0.5 5 20 40 40 40 1 0004 (ca 0 0 0. 1 O. 1 0. 1 0.1 0.1 1 1424 (ca 0 0 1 .5 10 15 20 1 0494 (ca 0 0 0 0 0 0 0 1.0160 (ca 0 0.2 1 3 5 8 10 1.0998 (ca. 0 0 0 0 0 0 0 Example 2 In a chemical plating bath of the following composition:

15 g./liter of cobalt chloride .15 g./ liter of nickel chloride 15 g./ liter of ammonium chloride 20 g./liter of sodium acetate 50 mg./liter of thiodiglycollic acid 3.5 g. of N-diethyl-borazane dissolved in 50 ml. 10

metihanol iron plates were provided with a Co-Ni-B coat- "irrq. The iron plates had an area of 1 dm. each. The composition of the coating was approximately 47% Co, "51% Ni and 2% B. The after-treatment of the plates 15 as well as the corrosion test were carried out as described in Example 1.

(a) 100 g./liter of potassium dichromate (b) 100 g./ liter of potassium dichromate 10 ml./ liter phosphoric acid D 1.84 The corrosion test was carried out as described in Example 1. The following values were obtained:

Rust as percent of surface Sample After- N o. G.-deposit CO-Ni-B/drn. treated Hours Days 0.5048 (ca. 811) 0. 2 0. 8 1 20 45 55 70 1.0052 (ca. 0 0 0.2 0.5 1 4 7 10 1.5070 (ea. 0 0 0 0.2 0.5 0.8 1 3 7 10 0.5281 (ca. 811) 0 0 0. 2 0. 6 1 4 8 12 16 20 1 0740 (ea. 15 0 0 0 0.2 0.3 0.4 0.5 0.0 0.7 0. 8 1.5166 (ca. 0 0 0 0 0 0 0 0 0 0.1

Example 3 Bust in percent of surface after 15 days Residing Bath G. Ni-B/dm time (ca. 1.1400 (ea. (ca. 1.0184 (ea. (ca. 1.0216 (ca. 15

(ea. 1.0264 (ea. (ea. 1.0486 (ca. (ca. 1.1020 (ea. 15p) (ca. 1.0130 (ca.

The samples were subsequently suspended for 150 hours in an aerosol chamber with 0.3% NaCl spray. During the duration of the experiment no further rust formation occurred.

Example 4 7 0 Iron plates were provided with a Ni-B layer as described in Example 1. The after-treatment of the plates took place at C. and with varying stays in aqueoussolntions of A non after-treated iron plate having a Ni-B coat ng of 2.0540 g. Ni-B/dm. showed after 12 days 4% rust (expressed as a percentage of the surface).

We claim:

1. A process for improving the corrosion resistance of metal coatings containing boron and a metal selected from the group consisting of Ni, Co, and Ni-Co-systems chemically deposited from a plating solution containing as essential ingredients a metal selected from the group consisting of Ni, Co, and Ni Co-systems and a borohydride which comprises treating the chemically plated surfaces with an aqueous solution containing a hexavalent chromium compound, the chromium compound being present in an amount between 1 to about 300 g./l. of chromic acid.

2. A process according to claim 1, wherein said aqueous solution additionally contains a member selected from the group consisting of phosphoric acid and soluble salts thereof, the phosphoric acid being present in an amount between about 1 and 20 g./l. of aqueous solution.

3. A process according to claim 1, which comprises effecting said treatment with said aqueous solution at a temperature between about 18 and about 100 C.

4. A process according to claim 1, which comprises effecting said treatment with said aqueous solution at a temperature of 40 C. and wherein said aqueous solution contains 200 g./l. of chromic acid and 5 g./l. phosphoric acid.

5. A process according to claim 1, which comprises efiecting said treatment with said aqueous solution at a temperature of C. and wherein said aqueous solution contains 200 g./l. of chromic acid.

6. A process according to claim 1, which comprises effecting said treatment with said aqueous solution at a temperature of 60 C., wherein said aqueous solution contains 200 g./l. chromic acid and 10 mL/l. phosphoric acid (D 1.84).

(References on following page) References Cited by the Examiner UNITED STATES PATENTS McLean et a1 148-616 X Ostander 1486.16 q Douty et a1 1486.16 X Rausch 1486.16

De Long et a1 '11713O X Hoke 117130 Deyrup. McLeod 117-130 X Lee 117130 JOSEPH B. SPENCER, Primary Examiner.

RICHARD D. NEVIUS, Examiner. 

1. A PROCESS FOR IMPROVING THE CORROSION RESISTANCE OF METAL COATINGS CONTAINING BORON AND A METAL SELECTED FROM THE GROUP CONSISTING OF NI, CO, AND NI-CO-SYSTEMS CHEMICALLY DEPOSITED FROM A PLATING SOLUTION CONTAINING AS ESSENTIAL INGREDIENTS A METAL SELECTED FROM THE GROUP CONSISTING OF NI, CO, AND NI CO-SYSTEMS AND A BOROHYDRIDE WHICH COMPRISES TREATING THE CHEMICALLY PLATED SURFACES WITH AN AQUEOUS SOLUTION CONTAINING A HEXAVALENT CHROMIUM COMPOUND, THE CHROMIUM COMPOUND BEING PRESENT IN AN AMOUNT BETWEEN 1 TO ABOUT 300 G./1. OF CHROMIC ACID.
 2. A PROCESS ACCORDING TO CLAIM 1, WHEREIN SAID AQUEOUS SOLUTION ADDITIONALLY CONTAINS A MEMBER SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID AND SOLUBLE SALTS THEREOF, THE PHOSPHORIC ACID BEING PRESENT IN AN AMOUNT BETWEEN ABOUT 1 AND 20 G./1. OF AQUEOUS SOLUTION. 